The invention is directed to a method and apparatus for inspecting the outer surface of a container such as a glass bottle for out-of-round condition.
In particular, the invention is directed to method and apparatus for inspecting the outer surface of a container using a phase detection technique wherein the phase difference between transmitted and received signals, such as acoustic, optical or microwave signals, is used to provide an indication of the magnitude of the out-of-round condition. The invention has particular application in the inspection of glass bottles for out-of-round condition.
Containers such as glass bottles are formed from molten material. Variations in the heat transfer condition required to produce a rigid container from the molten material may result in malformed containers. A common malformation occurs in the barrel or body portion of the bottle wherein this portion of the bottle is formed in an egg-shaped or other out-of-round condition.
An egg-shaped or out-of-round body condition is undesirable. In pressure containers, such as carbonated beverage bottles, the ideal body shape is cylindrical, i.e., round, to minimize stress. Variations from round result in stress which weakens the container. In labeling a container, an out-of-round condition causes lack of contact between the label and container as well as wrinkling of the label. Further, an out-of-round container is frequently oversized in one dimension, and this results in line jams during filling and processing of the container.
For years, the container processing industry has sought to produce a unit capable of measuring and automatically ejecting from line those containers that are out-of-round beyond tolerable limits. In general, such attempts employed sensors or transducers which mechanically contacted the container surface. Current rates at which containers are formed, however, are so great that it is not practical to maintain mechanical contact between the container and sensor. The use of light, low inertia mechanical sensors does not provide a practical solution to the problem because such sensors tend to become too fragile for survival in the operating environment.
Various acoustic inspection techniques are known for detecting flaws in or characteristics of an object. For example, U.S. Pat. No. 4,096,738 discloses a technique wherein a device ultrasonically tests glass containers by contacting a container and shattering the container if the container is defective. U.S. Pat. No. 4,099,418 discloses an acoustic inspection technique for determining the eccentric characteristics of a tube. At least two acoustic devices are positioned 90.degree. or more apart for the purpose of measuring and comparing container wall thicknesses at the locations of the devices. U.S. Pat. No. 3,289,468 discloses a technique wherein an acoustic transducer disposed along a radius of the object being inspected measures wall thickness. A signal is reflected off the outer surface and the inner surface of the object, with the resultant signals being processed to detect the time interval between reflected pulses.
Heretofore, there has been a need for an accurate and reliable out-of-round inspection unit capable of rapidly and reliably determining an excessive out-of-round condition in the operating environment of the container processing plant while being relatively simple to operate and service.